Windows 11 Latin locale strftime x format specifier behavior different than Windows 10

Question

Hi we are seeing a difference in strftime x format specifier behavior on Windows 11 when the locale is set to "la" or "la-VA" (Latin). The problem can be observed with either Visual Studio 2019 or 2022. See the following testcase

#if defined(_WIN32)  
#  include <windows.h>  
#else  
#  include <locale.h>  
#endif  
#include <iostream>  
  
int main()  
{  
    setlocale( LC_ALL, "la" );  
    char outstr[200];  
      
    struct tm t = {0, 0, 0, 1, 0, 0, 0};  
    t.tm_mon = 1;  
    t.tm_mday = 6;  
    t.tm_year = 70;  
      
    mktime(&t);  
      
   if (strftime(outstr, sizeof(outstr), "%x", &t) == 0) {  
       fprintf(stderr, "strftime returned 0");  
       exit(EXIT_FAILURE);  
   }  
   std::cout << outstr << std::endl;  
     
    return 0;  
};  

On Windows 10 the output is:

C:\dev>cl /EHsc test.cpp  
Microsoft (R) C/C++ Optimizing Compiler Version 19.29.30038.1 for x64  
Copyright (C) Microsoft Corporation.  All rights reserved.  
  
test.cpp  
Microsoft (R) Incremental Linker Version 14.29.30038.1  
Copyright (C) Microsoft Corporation.  All rights reserved.  
  
/out:test.exe  
test.obj  
  
C:\dev>test.exe  
06/02/1970  

On Windows 11 the output is:

C:\dev>cl /EHsc test.cpp  
Microsoft (R) C/C++ Optimizing Compiler Version 19.29.30038.1 for x64  
Copyright (C) Microsoft Corporation.  All rights reserved.  
  
test.cpp  
Microsoft (R) Incremental Linker Version 14.29.30038.1  
Copyright (C) Microsoft Corporation.  All rights reserved.  
  
/out:test.exe  
test.obj  
  
C:\dev>test.exe  
6 2 1970 gg  

Using GetLocaleInfoEx to query the LOCALE_SSHORTDATE of the locale showed on Windows 10 has the format "dd/MM/yyyy" and Windows 11 has "d M yyyy gg"

 #include <windows.h>  
 #include <iostream>  
      
 int main()  
 {  
     int   ret;  
     wchar_t buf[200];  
     wchar_t loc_name[] = L"la-VA";  
      
     ret = GetLocaleInfoEx((LPCWSTR)&loc_name,  
                           LOCALE_SSHORTDATE,  
                           (LPWSTR)&buf,  
                           sizeof(buf) / sizeof(*buf) );  
     printf("locale: %ls\n", loc_name);  
     printf("LOCALE_SSHORTDATE: %ls\n", buf);  
     return 0;  
 }  

I didn't find the "gg" datetime specifier in strftime documentation, however, I did find it in C# documentation noted here https://learn.microsoft.com/en-us/dotnet/standard/base-types/custom-date-and-time-format-strings#gSpecifier

strftime appears to not have the period and era information but instead of ignoring the specifier as documented in C#, it outputs the specifier. I think this is the core of my question, should "gg" be printed?

Answer 1

Hi, @Scott Zhong

For your reference: LOCALE_SSHORTDATE and Day, Month, Year, and Era Format Pictures

g, gg Period/era string formatted as specified by the CAL_SERASTRING value. The "g" and "gg" format pictures in a date string are ignored if there is no associated era or period string.

It doesn't look like an expected behavior. You can report the issue to Developer Community and post the link in the comment.
Best regards,

Minxin Yu

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Answer 2

Hi there,

strftime returns the number of characters placed in strDest and wcsftime returns the corresponding number of wide characters.

If the total number of characters, including the terminating null, is more than maxsize, both strftime and wcsftime return 0 and the contents of strDest are indeterminate.

As this is not the expected output you can try to raise this via the feedback hub so that the team can have a look and come out with a solution in upcoming builds.

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